24. Repellants
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24 Repellants We are cast out and this boat is our country now—and the sea is our refuge. —Joseph Conrad, 1897 His­ tori­ cally, human movement has of­ ten been motivated by negative phenomena, forces presenting incentives to leave a locale. These expulsive factors made life elsewhere—almost anywhere, perhaps—more attractive than remaining at home, at least for some members of the population. Fear and suffering were the basic emotions—of or from death, hurt, hardship, obligation, or shame— and reduction of physical, financial, or social insecurity was the goal. Here, we inventory some of the major classes of repellant phenomena. Earth Force: Physical-­ Geographic Factors Push factors include physical-­ geographic phenomena such as severe drought; soil erosion and fertility decline; and crops lost to pests or disease, to hurricanes, and to volcanic eruptions and their consequent mudflows, shade-­producing airborne ash, and lowered atmospheric temperatures. As an example of volcanic disaster, the catastrophic eruption on the Aegean island of Thera about 1628 BC may not only have disrupted civilizations and precipitated migrations, it may also possibly have given rise, at least in part, to the legend of Atlantis, which Plato placed in the Atlantic (his story, attributed to Egyptians, could conceivably be a conflation of the Thera episode and some notion of a transatlantic landmass as discussed in chapter 1). On New Britain, the San Cristobal eruption of circa 1600 BC was much, much larger than Krakatau’s of 1883, covering huge expanses with ash. Such catastrophic eruptions also occurred in the more distant past. In southeast­ ern Asia and Oceania, occasional drought-­ producing monsoon failures as well as great floods have repeatedly led to severe social and po­ liti­ cal disruptions and may well have triggered some overseas migrations. The periodic ENSO-­associated megadroughts of southeast­ern Asia (see chapter 3)1 would 260 / Chapter 24 not only have acted as a push factor, they would simultaneously have provided westerly winds for traversing the Pacific. In the Marquesas Islands, food shortages brought on by drought led to formation of great fleets carrying hundreds of refugees and great stocks of food and water, live animals, and young plants, sailing off to search for a new place to settle.2 Perhaps the best-­ known modern instance of the food-­scarcity phenomenon is the flight of huge numbers of Irish from the mid-­ nineteenth-­ century potato famine. Other physical-­ geographic phenomena include earthquakes and tsunamis. Among such disasters, one can point to the disappearance beneath the waves of the Peloponnese’s Mycenean port of Pavlopetri circa 1000 BC, the seismic sinking of the Anatolian port of Klazomenai in the sixth century BC, the down dropping of much of Egypt’s port of Alexandria and nearby Canopus and Hera­ kleion (exacerbated by deltaic subsidence) in AD 365, and the seismic subsidence of the harbor of Roman Palestine’s Caesaria, plus the post-­Columbian sinkings of the Lisbon, Portugal, harbor and Port Royal in Jamaica. In a few cases, large-­ scale tectonic activity has caused widespread coastal inundation. For example , since antiquity the subducting Af­ ri­ can tectonic plate has resulted in roughly 13 feet of subsidence along the North Af­ ri­ can littoral, dropping some important archaeological sites under the sea. Massive mudslides and the occasional radical shifting of the courses of great rivers (for example, China’s Huang He) also occasionally triggered migrations, as did pestilence. As seen in contemporary times, tsunamis have been highly disruptive in, and even very far from, earthquake-­ prone areas, especially around the Pacific. The Tōhoku region of Japan’s Honshu Island has experienced large earthquakes and tsunamis every 500 to 800 years—the latest, in 2011, which carried water 8 miles inland. North America’s Northwest Coast shows evidence of thirteen earthquake-­ tsunami impacts during the past 6,000 years. In AD 1076, a tsunami inundated up to 310 miles along the coast of South China.3 Seawater puts salt into the soil and, for a time, damages or kills wild vegetation and prevents successful farming, and gatherers and farmers are obliged to seek sustenance elsewhere. A Rising Tide Lifts All Boats: Eustatic and Sterical Sea-­ Level Changes A potentially important push factor that has only recently been receiving significant attention has to do with the seas themselves, that is, eustatically and sterically rising sea levels. As has long been widely recognized, with the melting of the continental ice sheets at the end of the Pleistocene epoch some 12,000 years ago...